Wireless handsets (cellular telephones) can generate interference with hearing aids that leads to audible noise. The Federal Communication Commission (FCC) will soon require that at least some of the wireless handsets offered by each wireless service provider meet certain standards aimed at reducing interference with hearing aids. These Hearing Aid Compatibility (HAC) standards stipulate that the electric and magnetic field strength within at least six squares of a nine square measurement grid centered on the speaker of a qualifying handset and spaced from the handset by 1 centimeter be below predetermined limits. FIG. 1 depicts a “candy bar” form factor wireless handset 100 with the aforementioned nine square measurement grid 102.
It has been found that it is particularly difficult to make “candy bar” wireless handsets that meet the FCC HAC requirements. Most currently available “candy bar” wireless handsets use internal antennas that are located either the bottom or top end of the handsets internal printed circuit board. Examples of internal antennas include the Planar Inverted “F” (PIFA) antenna and the more advanced Folded Inverted Conformal Antenna (FICA). Generally, internal antennas of wireless handsets use the ground plane of the wireless handset's internal circuit board and/or other conductive parts of the handset as a counterpoise in at least some operating bands (e.g., operating bands in the 800 MHz to 900 MHz range). Consequently, high electric field regions occur both near the antenna and at the opposite end of the handset (at the remote end of the counterpoise.) Such high electric fields are problematic for meeting the FCC HAC requirements.
Thus, what is needed is way to control the pattern of electric fields near the earpiece speaker of wireless handsets so that interference with hearing aids will be reduced and the FCC HAC requirements will be met.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.